AND THE ACTINIC CONSTITUTION OF THE ATMOSPHERE. 21 



But tliis rule is not always confirmed, on account of the intervention of what I 

 have called in another pa[>ei' i)lK'nomena of entanglement. These operate so that 

 one oxidizable body may involve another in the same decomposition which it 

 undergoes itself. But here we begin to sti-ay away from tiu; subject of this paper, 

 which is the actinic study of the atmosphere. I am content, therefore, to draw 

 from the great sum total of the results I have obtained the following conclusions: 

 The nature and the proportion of the oxidizable elements which living nature scat- 

 ters through the air, betray themselves in the solar combustion of oxalic acid, which 

 is the more feeble on the surface of the solution the more the radiations have met 

 with unstable elements to oxidize during their passage. The organic substances of 

 the atinosphei'e are thei'efore a pi'otection against too intense an action of the chemi- 

 cal rays at the surface of the soil, and the effect which they pro<luce is not only 

 measurable, but sometimes very great. In other words, we do not know what the 

 chemical power of solar light may be at its entrance into the atmosphere, but on a 

 level with the soil it is so impoverished that a thin layer of turpentine vapor, of 

 sulphate of rpiinine, or of any oxidizable substance, suffices to destroy it almost 

 completely. 



This conclusion has, however, another side to be considei'ed, which is, that 

 the atmosphere must at every moment l)e the seat of combustions, such that, on 

 the whole, all luminous radiations are utilized. I shall not insist here on the power 

 and the importance of the phenomena of oxidation which take place in the atmos- 

 phere and at the level of the soil, nor upon the general effect which they have on 

 sanitation over which they preside. 1 have published several memoirs on that sub- 

 ject,' to which I nuist be content to refer. I have there called attention to the 

 power of the solar I'ays on microbes, first weakening and then killing them, a 

 power which was first indicated, but incompletely proven, by Messrs. Downes and 

 Blunt.' I have, moreover, studied the iniiuence of the conditions of the medium 

 on the resistance of germs. All that has been done since, has only confirmed the 

 importance which I attached to light and to the chemical portion of the solar spec- 

 trum as principal agents in the hygiene of the globe. 



INFLUENCE OF INCREASE OF LATITUDE. 



This first problem, that of the possible influence exerted by oxidizable sub- 

 stances while in suspension in the atmosphere, having been sufficiently discussed in 



' Amiaks de Chimie et de Physique, 6th S., vol. v., May, 1885, and Comptcs Rendus, vol. c. and ci. 

 Annales de V Institut Pasteur, vol. i., p. 88. 



' The conclusions of these scholars had been opposed by Tyndall and by Jamieson, so that 

 when I took up the question anew, it had not yet met with a solution. It has found one to-day. 



